Variable illuminant



Nov. 26, 1929. G. M. WRIGHT ET AL 1,737,288

VARIABLE ILLUMINANT Filed Feb. 20. 192.6

INVENTOR G.M.WR\GHT AND R. N. VYVYAN A61 /adCu4w A ORNEY Patented Nov. 26, 1929 3 umrsofsmras PATENT OFFICE GEORGE MAURICE 'WBI GH'LOI CHESTERFIELD, AND RICHARD NORMAN VYVYAN, OI EAIPSTEAD, LONDON, ENGLAND, ASSIGNORS T RADIO CORPORATION 01' AMERICA,

4 oo'aromrron or DELAWARE VARIABLE ILLUMINANT lpplicationnled February 20, 1926, Serial No. 89,565, and in Great Britain March 6, 1925.

An object of our invention is to provide a variable source of radiant energy.

Another object of our invention is to provide a source of radiant energy and means 5 for producing rapid variations therein.

Another object of our. invention is to provide a source of radiant energy adapted for combination with the receiving apparatus of a picture transmission system.

Another object of our invention is to provide a source of radiant energy comprising means for producing ultra-rapid variation thereof.

Another object of our invention-is to provide a source of radiant energy of the Xray type with an auxiliary means for producing rapid changes in radiation intensity therefrom by the action of small amounts of control energy.

Another object of our invention is to provide a source of radiant energy having a control member adapted to vary the intensity of radiation therefrom by the application of small control potentials.

In processes and systems for the transmission of pictures by means of signal channels, using means for converting the variations of light intensity in a picture into fluctuating electric currents, for transmitting the currents as signal currents and re-converting at a remote point into fluctuating light intensities, one of the most serious difficulties has been found to be that of converting the fluctuating signal currents into fluctuating ra diant energy for application to a sensitive surface. Moving mirrors,-string galvanometer type li ht valves, pens, gas filled glow tubes and the like have been employed, but all such devices have been found to be slow in functioning and incapable of following the signal current fluctuations at hi h speeds.

The limitation upon the speed of transmis sion of pictures thus occurs mainlyin the con trol of the light intensity at the receiving apparatus.

According to our invention we employ an X-ray emitting device containing control means responsive to the received electrical variations for controlling the intensity of the i0 emitted rays.

' Preferably we employ an X-ray tube provided with a heated cathode and a controlling grid between the cathode and the target. The potential variations in the receiving circuit are transferred by a suitable amplifier to this grid, and thereby, the electron flow in the X-ray tube, and consequently the intensity of the emitted X-rays will repeat the same variations.

The X-rays may then be caused to act through suitable slits or other means for maintaining synchronism with the sending apparatus either upon a photographic surface, or, for television, upon a fluorescent screen.

When this invention isused in conjunction with the invention described in our copending application Serial No. 89,564, filed February 20, 1926, and assigned to the Radio Corporation of America, a transmitting and receiving system of extreme rapidity is obtained, since the controlling means are electrical instead of mechanical.

Other objects and structural details of my invention will be apparent from the following description when read in connection with the accompanying drawings, wherein:

Fig. 1 shows diagrammatically a Vacuum tube of the X-ray type, modified by the addition of the grid of our invention so as to be suitable for use for the transmission of pictures.

Fig. 2 shows a transmitting system, and

Fig. 3 shows a receiver in which the tube shown in Fig. 1 is used to change electrical energy impulses to X-rays of varying intensity.

Referring to Fig. 1 of the drawing, 1 is a target anode and 2 a heated cathode within a focussing screen of the kind usually employed in X-ray tubes of the so-called Coolidge type. 3 is a grid projecting into the path of the rays between the cathode and the target.

The potential variations in the receiving circuit are applied to the grid and thereby serve to control the intensity of the emitted X-rays which are caused to act through suitable slits or the like upon a sensitized surface or upon a fluorescent screen.

The grid 3 thus performs the function which is somewhat similar to the function of the grid in the customary triode, in that it controls the electron stream. Its function is however, broadly different in that control 0 the current flowing in the connected circuits is purely incidental to a control of the energy in the electron stream and the ener with which the stream impinges u on t e target 1 to produce X-rays. he unction of the electron stream is further broadly new in that it forms a part of a picture transmission system for the direct control of the radiation intensity of the radiant enwhich directly reproduces the picture. 11 Fig. 2 P is a hoto-electric cell which receives varying lig t, due to the light and shade of the picture to be transmitted, said icture being passed between a source of light (not shown) and the cell in any well known way. A is an amplifier to which the output from the photo-electric cell is fed, the magnified out ut from the said amplifier bein applied etween the grid and cathode of a requency modulator valve F. Included in the anode circuit of the valve F is a coil which is coupled at'K to part of the oscillatory circuit of the master oscillator M. The variation of the potential between the grid and cathode of the modulator valve F causes corresponding variation in the anode cathode resistance of said valve and these in turn cause corresponding variations of frequency in the master oscillator M. These frequency variations are then applied to the circuits of a wireless transmitter T, and are radiated as waves of varying length.

It has been found that ing the value of the coupling K and by selectin for the oscillator M a valve of suitable c aracteristics, a linear relationship between the intensity 'of light falling upon the photo-electric cell and the frequency of the radiated wave may be obtained.

In Fig. 3 N is a receiving aerial which is coupled to an amplifier A arranged in any own manner to limit the high frequency currents down 'to the minimum intensity occurring durin a fading period, so that the out ut from t e said amplifier has substantial y the same amplitude for all frequencies. This output is applied through a transformer, between the 1d and cathode of the valve D in whose ano e circuit is included the inductance L of low resistance and of impedance to the fluctuating currents flowing through it, which is small as compared to the anode cathode impedance of the valve.

With this arrangement the otential difference across the inductance IE will be substantially proportional only to the frequency of the incoming si als. These otential differences are app led to a recti or R in own manner, and the currents resulting therefrom are passed through a low pass filter S which removes high requency comby suitably adj ustponents. The output from the filter S will then be direct current of intensity substantially proportional to the frequency of the received wave, and may be ap lied across the grid and filament of the )E-ray tubes shown in Fig. 1 of the drawings and thus the X-ray radiation of the X-ray tube will be controlled as hereinbefore described.

By the apparatus of our invention we provide an X-ray tube having a control means which is responsive to small fluctuations in electrical energy and whereby a fluctuating stream of radiation energy, suitable to effect a photographic plate or a fluorescent screen and thereby to produce an image, is obtained.

By means of our invention we are enabled to produce a picture transmission system in which the limitation imposed upon the speed of transmission by the inertia of the illuminant control means is removed and whereby much higher speed of transmission is ob tained.

While we have shown but one embodiment of our invention in the fore oing drawings and descriptions, it is capa le of various modifications therefrom without depar in from the spirit thereof, and it is desired therefore that only such limitations shall be imposed thereon as are required by the prior art or indicated by the appended claims.

We claim as our invention:

1. The method of producing a visible indication of picture impulse signals in a system including an X-ray tube for producing a glow for sensitizing the recording surface in accordance with the received signalimpulses, which comprises, receiving and amplifyin signals, limiting the strength of the received signals to a pre-determined value, rectifyin the received signals, and controlling the X ray radiation of said X-ray tube in accordance with the said signals of limited intensity.

2. The method of producing a visible indication of picture impulse signals in a system including an X-ray tube for producing a flow for sensitizing a picture recording surface in accordance with the frequency of received signal impulses, which comprises, receiving and amplifying signals of frequencies varying in proportion to the intensity of light and shadow on' elemental areas of picture surface, limiting the strength of the received signal im ulses to a minimum intensity occurring d iiring fading periods, converting the variable frequency received impulses into direct current impulses of intensity proportional to the frequency of the received signal impulses, and controlling the X-ray and radiation of said X-ra tube to vary the same in accordance with t e intensity of said direct current impulses.

GEORGE MAURICE WRIGHT. RICHARD NORMAN VYVYAN. 

